Removal of catalyst residues from olefin polymers



Oct. 18, 1966 J. s. scosem REMOVAL OF CATALYST RESIDUES FROM OLEFIN POLYMERS Filed Feb. 19, 1962 lllllllillllllllllll mm hm INVENTOR. J. S. SCOGGIN A TTORNEV5 @m vm ML u zmoomgz in the chain.

United States Patent "ice 3,280,090 REMOVAL (it CATALYST RESIDUES FROM GLEFIN PQLYMERS Jack S. Scoggin, Bartlesville, 0kla., assignor to Phillips Petroleum Company, a corporation of Delaware Filed Feb. 19, 1962, Ser. No. 174,002 14 Claims. (Cl. 26093.7)

This invention relates to the production of polymers of mono-l-olefins. In one aspect, it relates to a process for producing polymers having a low ash content and a desirable color and heat stability. 'In another aspect, it relates to a process for treating polymers prepared in a mass polymerization so as to substantially reduce the ash content of the polymers.

Various reactions for polymerizing olefins are described in the literature, and the polymerizations are usually carried out in the presence of catalysts. One type of catalysts which has been widely used in the polymerization of monoolefins, particularly ethylene, consists of an organometal compound, e.g., triethylaluminum, and a compound of a heavy metal, e.g., titanium tetrachloride. When certain olefins, such as propylene, are contacted with such a catalyst, there is obtained a polymer containing greater or lesser amounts of a fraction which is crystalline and which is characterized by a certain regularity of molecular structure. Thus, a polypropylene molecule can be considered as a chain of Z-carbon units with a methyl side group attached to every other carbon Certain polymers of this type are characterized by the "fact that they contain series of such monomer units in which all the methyl side groups are oriented in space at the same position or at the same angle with respect to the tertiary carbon atoms to which they are attached. The portion of the polymer having this regular structure is highly crystalline and is generally referred to as isotactic polypropylene. It is recognized that this highly crystalline polypropylene is preferred for most practical applications.

A well-known procedure for preparing isotactic polymers of mono-l-olefins, such as propylene, involves the polymerization of propylene with a catalyst system comprising an alkylaluminum compound and titanium trichloride. One of the problems encountered with polymers prepared by such processes concerns the presence in the products of catalyst residues or ash-forming ingredients. The ash content of a product refers to the inorganic constituents which are present in the polymer in unidentified form and which produce ash when the polymer is burned. The presence of these catalyst residues in the polymer adversely affect the color and heat stability of the polymer, as well as its electrical properties. In one process proposed for the polymerization of mono-l-olefins,

the olefin is polymerized in a mass system wherein the propylene is in liquid phase and the polymerization is conducted without the addition of more than small amounts of an inert diluent. In such processes, the only inert diluent present in the polymerization zone is that which may be present in the feed or that which may be used in the introduction of the catalyst. Because no extraneous diluent is present when using the mass polymerization technique, the polymer often contains a larger quantity of catalyst residues than when the same system Patented Oct. 18, 1966 is used in the presence of a diluent. The conventional method employed to remove catalyst residues from polymers prepared by these processes is to initially separate the polymer from the diluent or, in the mass polymerization process, from the monomer. Thereafter, the separated polymer is treated With a washing agent which is usually an alcohol, such as isopropyl alcohol. While this treatment of the polymer is quite effective in reducing the ash content of the polymer, the method has certain disadvantages, particularly in a continuous polymerization process. When using a material such as an alcohol, an entirely different type of material is thereby introduced into the system. As a result, it becomes necessary to provide special equipment for the recovery and purification of the alcohol. From an economical standpoint, the use of a material such as alcohol to treat the polymer is unsatisfactory. Furthermore, the presence of the alcohol in the system presents difficulties in handling because of leakages and evaporation. The present invention is concerned with a method for producing polymers of mono-Lolefins in which these difficulties are overcome.

It is an object of the present invention to provide an improved process for producing polymers of mono-1- olefins having a low ash content.

Another object of the invention is to provide a process for treating polymers prepared in a mass polymerization in order to remove catalyst residues associated therewith.

A still further object of the invention is to provide a process for polymerizing mono-l-olefins wherein the polymerization efiluent containing liquid monomer and solid polymer is treated so as to remove catalyst residues.

A still further object of the invention is to provide a process for treating a stream containing solid polymer, liquid monomer and the polymer soluble in the monomer so as to recover a solid polymer having a reduced ash content.

Various other objects, advantages and features of the invention will become apparent to those skilled in the art upon consideration of the accompanying disclosure and the drawing which is a schematic flow diagram illustrating a preferred embodiment of the invention.

The present invention is concerned with an improvement in a process for polymerizing a mono-l-olefin with a catalyst comprising an organometal compound and a metal salt in the substantial absence of a hydrocarbon diluent and under conditions such that the monomer serves as the diluent and a solid polymer in particle form is obtained. Broadly speaking, in a mass polymerization process wherein a liquid mono-l-olefin is contacted with a catalyst capablefof polymerizing the olefin under polymerization conditions so as to form solid polymer and wherein an efliuent containing solid polymer, catalyst residues and liquid olefin is recovered from the polymerization, the improvement resides in the steps which comprise (l) mixing the effluent with a diketone under conditions such that the olefin remains in the liquid phase, (2) recovering the thus treated effluent and washing same in a countercurrent contacting procedure with a low boiling hydrocrabon, preferably the same olefin used in the polymerization, under conditions such that the hydrocarbon remains in the liquid phase, and (3) thereafter recovering a solid polymer having a reduced ash content, i.e., substantially free of catalyst residues. When operating in this manner, it has been found that the polymer product has an ash content of 0.01 weight percent or less. Such a polymer meets the requirements as to color and heat stability and possesses satisfactory electrical properties. Furthermore, the product obtained by the present process is superior as regards these properties to a polymer which is purified by conventional methods using alcohols or other treating agents. It is also seen that the present process does not introduce foreign materials into the system, which require additional equipment for their separation and recovery. In a commercial operation, this is, of course, a very important advantage.

As mentioned hereinbefore, the polymers which are treated in accordance with the present process are prepared from mono-l-olefins. The present invention is particularly applicable to the treatment of isotactic polymers which are prepared by polymerizing mono-l-olefins containing at least 3 carbon atoms and preferably not more than carbon atoms. Examples of such monomers include propylene, l-butene, l-pentene, 3-methyl-l-butene, and the like. Furthermore, it is to be understood that polyethylene can be treated by the present process in order to remove catalyst residues. It is to be understood also that mixtures of two or more monomers can be employed in the polymerization to produce copolymers which are then treated by the present process. In a preferred embodiment of the invention, propylene is utilized as the monomeric material.

a mass polymerization and under conditions such that solid polymer in particle form is produced. Catalyst systems suitable for use can be broadly defined as comprising an organometal compound and a metal salt. A particularly suitable catalyst is one which comprises (a) a compound having the formula R MX wherein R is an alkyl, cycloalkyl or aryl radical or combinations of these radicals, such as alkaryl, aralkyl and alkylcycloalkyl, X is hydrogen or a halogen, including chlorine, bromine, iodine and fluorine, M is aluminum, gallium, indium or thallium, n is from 1 to 3, inclusive, m is from zero to 2, inclusive, and the sum of m and n is equal to the valence of the metal M, and (b) a halide of a metal of Groups IV-B, VB, VIB or VIII. The hydrocarbon radicals which can be substituted for R in the aforementioned formula include radicals having up to about 20 carbon atoms each. Radicals having carbon atoms or less are preferred since the resulting catalyst composition has a greater activity for initiating the polymerization.

Examples of compounds corresponding to the formula R MX which can be employed include trimethylaluminum, triethylaluminum, triisobutylaluminum, tri-n-butylaluminum, tri-n-pentylaluminum, triisooctylaluminum, tri-n-dodecylaluminum, triphenylaluminum, triethylgallium, triphe'nylgallium, tricyclohexylgallium, tri-n-butylindium, triethylthallium, diethyla-luminum hydride,

CH AlCl (CH AlCl, C H AlCl (C H AlCl 4 9)2 a 17 2, 3 7)2 e 11)2 (cyclohexane derivative), (C H )GaBr (benzene derivative, CzgHnGHBI'z, (C H GaF, (C6H5)2II]C1 (benzene derivative), C3H1I7IH'F2, (C H )InBr (cyclohexane derivative), 3 methylcyclohexylaluminum dichloride, 2- cyclohexylethylgallium dichloride, p-tolylberyllium iodide, di-(3 phenyl-1-methylpropyl)indium fluoride, 2-(3-isopropylcyclohexyl)ethylthallium dibromide, and the like.

The metal halide component of the catalyst system is preferably a halide of a Group IV-A metal, i.e., titanium, zirconium, hafnium and germanium. However, it is to be understood that halides of metals of the other groups specified above, such as vanadium, molybdenum,

such as titanium trichloride, in the polymerization.

The preferred catalyst system employed in the polymerization comprises a dialkylaluminum chloride and titanium trichloride, the latter compound preferably being prepared by reduction of titanium tetrachloride in the presence of aluminum. The reduction product is preferably a complex having the formula 3TiCl -AlCl The reduction reaction is usually carried out at an elevated temperature, for example, at a temperature in the range of 360 to 600 F., preferably from 375 to 450 F.

The amount of catalyst employed in the polymerization can vary over a rather wide range and will depend at least to a certain degree upon the particular catalyst system utilized. However, the determination of the actual amount of the catalyst employed in any particular polymerization is well within the skill of the art. In general, the mol ratio of the organometal compound to the metal salt falls within the range of 0.02 to 50 mols. When employing the preferred catalyst system, the mol ratio of the dialkylaluminum halide to the titanium trichloride complex usually ranges from 1.0:0.005 to 1.0:50u0, preferably 10:01 to 1.01100. The amount of the dialkylaluminum halide used should be at least 1.0 10" gm./ gm. of monomer and can be as much as 25 10 gm./ gm. of monomer. The amount of titanium trichloride complex employed would generally be in the range of 1.5 lO to 10 10- gn1./gm. of monomer.

Although not essential to the conduct of the polymerization, it is often desirable to carry out the polymerization in the presence of elemental hydrogen. When so operating, hydrogen is added in an amount suficient to provide from 0.15 to 0.40 mol percent hydrogen in the liquid mono-l-olefin phase in the polymerization zone. By operating in this manner, the productivity of the catalyst is increased and certain properties of the polymer, e.g., flexural modulus, are improved.

The diketones suitable for use in the practice of the present invention include alpha-diketones and beta-diketones. These diketones can also be defined as being selected from the group consisting of compounds having the formulas:

wherein R and R are hydrocarbon radicals, such as alkyl, cycloalkyl and aryl. Examples of suitable alpha-dike- .tones include the following: 2,3-butanedione, 2,3-pentanedione, 3,4-hexanedione, 4-methyl-2,3-pentanedione, 3,4-heptanedi-one, 5-methyl-2,3-hexanedione, 2,5-dimethyl-3,4-hexanedione, 2,2,5,5 tetramethyl-3,4-hexanedione, 1,2-cycl0pentanedione, 3 methyl-l,2-cyclopentanedione, 1,2-cyclohexanedione, bibenzoyl, bi-Z-furoyl, methylphenylglyoxal, phenylbenzylglyoxal, 4,4'-dimethoxybenzil, and the like. The following are examples of suitable beta-diketones: 2,4- pentanedione (acetylacetone), 2,4- hexanedione, 2,4-heptanedione, 5-methyl-2,4-hexanedione, 2,4-octanedione, 5,5-dimethyl-2,4-hexanedione, 3-ethyl- 2,4-pentanedione, 3,3-diethyl 2,4 pentanedione, 2,2-dimethyl-3,5-nonanedione, 1 cyclohexayl-1,3-butanedione, 5,5-dimethyl-1,3-cyclohexanedione, l phenyl-1,3-butanedione, 1-(4-biphenylyl) 1,3 butanedione, 1-phenyl-1,3- pentanedione, 1-phenyl-5,5-dimethyl 2,4 hexanedione, 1,3-diphenyl-1,3-propanedione, 1,4-diphenyl-1,3-butanedily applicable to the treatment of polymers of mono-lolefins prepared by mass polymerization, utilizing a catalyst capable of polymerizing the monomer to a solid polymer under the conditions employed. As used herein, the term mass polymerization is used to designate a polymerization which is conducted with the monomer in liquid phase and without the addition of more than small amounts of an inert diluent. The expression small amounts of an inert diluent is intended to mean such amounts of inert diluent as may be introduced into the polymerization zone by way of inert material in the monomer feed and inert diluent employed for ease of handling the catalyst components.

Referring now to the drawing, propylene is charged to reactor It? through line 11. Prior to use in the polymerization, the propylene is treated by conventional methods in order to remove contaminant such as oxygen, CO and moisture. It is also the usual practice to purge the reactor with an inert gas, such as nitrogen, in order to remove such contaminants prior to commencement of the polymerization. Lines 12 and 1.3, respectively, provide means for charging the catalyst ingredients, namely, the titanium trichloride complex and the diethylaluminum chloride, to the system. It is noted that line 12 is connected to line 11 so that the titanium trichloride enters the reactor along with the liquid propylene. As mentioned above, it has been found to be advantageous to conduct the polymerization in the presence of hydrogen. As shown, the hydrogen enters the propylene feed line through line 14 and is charged to the reactor along with the liquid propylene.

The reactor illustrated in the drawing is a loop-type reactor which comprises two loops. Each loop i composed of two straight legs 16 which may conveniently be in the form of elongated pipe sections. The ends of the legs of the reactor are conveniently interconnected by means of Ls 17 so as to provide a continuous flow path through the reactor. The reactor is furnished with an impeller 19 which is operatively connected to a turbine 21. The operation of the impeller provides motive force for flowing the materials through the loop reactor. The

I vertical legs of the loop reactor are encompassed by heat exchange jackets 22 which are interconnected by means of lines 23. Line 24 connected to the heat exchange jacket associated with one of the outer legs provides means for introducing a coolant such as water. The coolant flows through the heat exchange jackets at a temperature and at a rate such as to maintain a desired polymerization temperature in the reactor. The coolant is removed from the reactor system by means of line 26 which is connected to the other outer leg of the reactor. Although it is often preferred to employ a loop-type reactor, it is to be understood that the polymerization can be conducted in any suitable polymerization zone, such as in a closed reaction vessel provided with a stirring means.

The conditions employed in conducting the polymerization will vary somewhat depending upon the mono-l-olefin utilized. The polymerization temperature is generally in the range of zero to 160 F. In the polymerization of ethylene, a temperature in the range of zero to 45 F. is usually employed. In the case of propylene, the temperature in reactor can vary within the range of 90 to 160 F. When polymerizing a higher olefin, such as 1- butene, a lower polymerization temperature is used, e.g., 86 F. or lower. In the polymerization of olefins containing 5 carbon atoms, still somewhat lower temperatures are utilized, e.g., about 75 F. or lower. In general, the polymerization is conducted at a temperature such that solid polymer in particle form is obtained in the polymerization. The actual amount of solid polymer formed is also dependent upon the particular catalyst system used. It has been found that the preferred catalyst system as described above produces a very high percentage of solid polymer with a minimum formation of soluble polymer. The pressure employed in reactor 10 is sufiicient to maintain the reactants in the liquid phase, e.g., a pressure in the range of 275 to 1000 p.s.i.g. The maximum pressure used is only limited by practical considerations, although it is generally undesirable to exceed a pressure of 2000 p.s.i.g. When polymerizing ethylene, the lower limit of pressure is about 425 p.s.i.g. at a polymerization temperature of about 0F. In the case of the polymerization of propylene, the lower limit of pressure is about 225 p.s.i.g. at a polymerization temperature of about 90 F. In the case of the higher olefins the lower limit of pressure will be somewhat lower. The pressure desired in reactor 10 can be conveniently regulated by an automatic control means as will be discussed more in detail hereinafter. The residence time in reactor 10 can range from about 1 to about 5 hours, with a residence time of about 3 hours being preferred.

The eflluent stream recovered from reactor 10 through line 27 comprises solid polymer, catalyst residues, soluble polymer and liquid propylene. The stream usually contains in the range of 25 to 40, preferably 35, weight percent solid polymer. After removal of the eflluent through line 27, it is passed through indirect heat exchange means 28 prior to introduction into a lower portion of contact tank 29. In the heat exchange means, the efiluent is heated to a temperature which is slightly higher than the temperature employed in reactor 19. Although it is within the contemplation of the invention to introduce the efiluent directly into the contact tank without prior heating, it has been found that improved results as regards catalyst removal are obtained if the temperature maintained in the contact tank is slightly higher than the polymerization temperature. In the case of polypropylene, the eflluent in line 27 is usually heated to a temperature in the range of to F. In the case of efiluents containing higher olefin polymers, a somewhat lower temperature can be used. The pressure in contact tank 29 is sufficient to maintain the propylene in the liquid phase, and it is usually substantially the same as the pressure in reactor 10. Line 30 provides means for introducing a diketone, such as acetylacetone, into the contact tank. It is noted that line 30 is connected to line 27 so that the acetylacetone enters the contact tank along with the effiuent.

In contact tank 29 the acetylacetone is thoroughly mixed with the efiluent from reactor 10. The contact tank depicted in the drawing comprises an enclosed vessel having baflle members 31 disposed in the upper and lower portion of the tank. The baflle members are attached to the walls of the tank and are each provided with a central opening through which the shaft of stirring means 32 passes. The positioning of the baffle members in this manner in effect divides the contact tank into upper, intermediate and lower sections. Each of these sections is provided with a stirrer 33 which is attached to the shaft of stirring means 32.. It has been found that particularly good contact is obtained between the acetylacetone and the effluent from reactor 10 when utilizing this specific structure. However, it is to be understood that it is not intended to limit the invention to any particular contact tank and that any enclosed vessel provided with a suitable stirring means can be employed.

The diketone, e.g., acetylacetone, can be introduced into line 27 by itself, or it can be added as a solution T? in a hydrocarbon which is inert to the reactants. However, the acetylacetone is preferably added as a solution, for example, a 1 percent solution, in the monomer. The amount of treating agent added in this manner may range from 1 to 5 times the stoichiometric equivalent, based on the amount of catalyst present. The contact time in contact tank 29 can vary within rather wide limits, e.g., from 5 minutes to 1 hour. However, it is usually preferred to use a contact time in the range of 20 to 30 minutes.

As previously mentioned, heat exchanger 28 provides means for heating the efiluent from reactor prior to its introduction into contact tank 29. As an alternative and often preferred procedure, line 34 provided with indirect heat exchange means 36 furnishes a means for increasing the temperature in the contact tank. When using this procedure, a low-boiling hydrocarbon is heated in heat exchanger 36 and then passed into the contact tank in order to raise the temperature therein to a desired level. As the low-boiling hydrocarbon, it is usually preferred to employ the monomer, e.g., propylene. However, it is within the scope of the invention to use a parafiinic hydrocarbon containing from 4 to 6 carbon atoms per molecule, such as n-pentane or n-hexane. This method of operation is often preferred because it obviates any danger of agglomeration of the polymer particles which may occur when the effluent is directly heated in heat exchanger 23.

The treated effiuent is withdrawn from an upper portion of contact tank 29 through line 37 and then passed into the upper portion of wash tank 33. It is preferred to introduce the effluent into a lower portion of the contact tank and to withdraw the treated efiruent from an upper portion of the tank since this method of operation ensures good contact between the solid polymer particles and the acetylacetone. As shown in the drawing, the wash tank comprises an enlarged upper portion 39 and a smaller lower portion 41. This type of structure is preferred although it is within the scope of the invention to employ a wash tank having a uniform cross section. Line 42. provides means for introducing wash liquid into the lower portion of the wash tank. Although various light hydrocarbons, particularly paraffinic hydrocarbons containing from 4 to 6 carbon atoms per molecule, such as npentane, can be employed as the wash liquid, it is preferred to utilize the monomer, e.g., propylene, for this purpose. Furthermore, because of the improved results obtained with propylene, it is not to be implied that the use of propylene is equivalent to the use of a material such as pentane as the wash liquid. It is also within the scope of the inventon to employ a mixture of the monomer and r a light hydrocarbon as the wash liquid. The efiiuent entering the wash tank through line 37 flows downwardly therethrough and contacts the liquid propylene in countercurrent flow. The liquid propylene in contacting the solid polymer removes catalyst residues, and the solid polymer settles into the bottom of the wash tank. This settling of the polymer is facilitated by providing a wash tank with an enlarged or expanded upper portion 39. The ratio of the cross sectional area of the enlarged upper portion to the cross sectional area of the lower portion of the wash tank is usually in the range of 1.5 to 2.5. When the wash liquid reaches the enlarged upper portion of the wash tank, its velocity is decreased, thereby causing solid polymer contained in the propylene to fall toward the bottom of the tank. In general, the velocity of the wash liquid in the enlarged upper portion is maintained at the minimum value which is consistent with efllcient removal of catalyst residues. This manner of operation conserves the amount of wash liquid used and reduces to a minimum the amount of polymer carried out of the wash tank in the overhead stream. The velocity of the wash liquid in the enlarged upper portion of the wash tank is usually in the range of 0.5 to 2.0, preferably from 0.2 to 1.0, feet per minute. The ratio of the amount of wash liquid to polymer, on a weight basis, is generally 0 ea in the range of 5:1 to 25:1. Actually, the upper limit is not critical, being limited only by the capacity of the column. However, as regards the lower end of the range, there must be enough wash liquid to provide good contacting and a hindered settling eifect in the column.

The overhead stream recovered from wash tank 38 through line 43 contains propylene, soluble polymer, catalyst residues and a small amount of solid polymer. The overhead stream is passed into cyclone separator 44, the underflow from which contains the solid polymer. The solid polymer separated in cyclone separator 44 is returned to the wash tank by means of line The overflow from cyclone separator 44, which is withdrawn through line 47, contains propylene, soluble polymer and catalyst residues. This stream can be further treated in order to recover the propylene for further use in the process. The overhead stream is withdrawn from the wash tank at a rate such as to maintain a predetermined pressure in reactor 10. This is accomplished by means of motor valve Stl which is positioned in line 47. Valve 50 is operatively connected to pressure recorder controller 52 which is preset at the pressure to be maintained in reactor 10. The controller receives a signal from pressure transmitter 53 which is connected to line 11. Since line 11 is connected to reactor 10, the signal received by the controller corresponds to the pressure in the reactor. In the operation of the control system, if it is desired to maintain a pressure of 350 p.s.i.g. in reactor 10, controller 52 is given this setting. Now if the pressure in reactor 10 rises to 360 p.s.i.g., pressure transmitter 53 transmits a signal proportional to this pressure to controller 52. Controller 52 then operates motor valve 50 so as to increase the degree of opening of this valve. As a result, the rate of withdrawal of the overhead stream from the wash tank is increased, thereby lowering the pressure in the entire system. When the pressure in reactor 10 has decreased to 350 p.s.i.g., the controller operates Valve 50 so that the overhead stream from the wash tank is withdrawn at a rate such as to maintain this pressure. When the pressure in reactor 10 is lower than that which it is desired to maintain, the opposite sequence of events occurs and the amount of the overhead stream withdrawn from the Wash tank is decreased.

The temperature maintained in the wash tank is generally somewhat lower than that in the contact tank. This results from the fact that the propylene charged through line 42 is generally at a comparatively low temperature, e.g., F. and below. The pressure maintained in the Wash tank is sufficient to maintain the propylene in the liquid phase.

As mentioned above, the solid polymer in the wash tank settles to the bottom of the tank. As a result of this settling, the slurry of solid polymer in propylene recovered through line 48 generally contains up to about 50 weight percent solids, e.g., from 40 to 50 weight percent. The slurry of polymer in propylene is withdrawn from the Wash tank through a suitable flow control means, such as cyclically operated motor valve 4-9. This valve is operatively connected to timer 51 which controls the frequency of the valve cycle. The slurry can be withdrawn from the wash tank at any desired rate merely by adjusting the setting of the timer. It is preferred to utilize a cyclically operated motor valve which opens, e.g., every 10 to 30 seconds for a short period of time, e.g., of about 1 second. This type of operation creates instantaneous pressure and velocity changes in the column, thereby causing turbulence and a concomitant shearing of the polymer particles. As a result, the efiiciency of the washing action is greatly increased. It is also within the scope of the invention to control the operation of the timer by means of a solids level controller 55 which is operatively connected to the lower portion of the wash tank and to the timer. When utilizing this arrangement of apparatus, the timer operates motor valve 49 so that a Table Stream No l1 14 12 13 27 30 34 37 Propylene to Hydrogen to TiCl to DEAC 1 to Reactor Acetyl Pentane to Contact tank reactor reactor reactor reactor efliuent acetone contact tank effluent Hydrogen Propylene r. Propane Aeetyl acetone n-Pentane Soluble polymer. Polypropylene DEAO 1 Titanium trichloride Catalyst residues- Hydrogen chlorid Ethane Inert gas Total, lb./sd 275, 076

Stream N0 43 42 Wash tank overhead Propylene to wash col.

Washed polymer to flash tank Flash tank overhead Inert gas to purge conveyor Polymer to process Purge conveyor ofigas Hydrogen r Titanium trichloride Catalyst residues Hydrogen chloride Ethane Inert gas Total, lb./sd 304, 927

tions and modifications are clearly believed to come,

within the spirit and scope of the invention.

I claim:

1. In a continuous propylene mass polymerization process wherein a liquid propylene is contacted in a polymerization zone with a catalyst formed by mixing materials comprising (a) a compound having the formula R MX wherein R is selected from the group consisting of alkyl, cycloalkyl and aryl radicals, X is selected from the group consisting of hydrogen and a halogen, M is selected from the group consisting of aluminum, gallium, indium and thallium, n is from 1 to 3, inclusive, m is from 0 to 2, inclusive, and the sum of m and n is equal to the valence of the metal M, and (b) a halide of a metal selected from the group consisting of metals of Groups IV-B, V-B, VI-B, and VIII, under polymerization conditions so as to form solid polymer in particle form and wherein an effluent containing solid polymer, catalyst residues, and liquid propylene is recovered from said polymerization zone, the improvement which comprises introducing said efiluent into a contact zone; mixing said effluent in said contact zone with a diketone selected from.

the group consisting of compounds having the following formulas:

R- I -("JR' and a wash liquid comprising a low boiling hydrocarbon into a lower portion of said wash zone; contacting said treated efiluent with said low boiling hydrocarbon in said wash zone in countercurrent flow under conditions such that said low boiling hydrocarbon and said propylene remaifi in liquid phase; withdrawing from an upper portion of said wash zone a stream comprising propylene, low boiling hydrocarbon, soluble polymer and catalyst residues; and recovering from a lower portion of said wash zone a stream comprising low boiling hydrocarbon and solid polymer substantially free of catalyst residues at a rate sufficient to maintain a desired level of polymer solids in said lower portion of said wash zone.

2. The process accordingto claim 1 in which said wash liquid consists essentially of propylene.

3. The process according to claim 1 in which said wash liquid consists essentially of n-pentane.

4. The process according to claim 1 in which said wash liquid consists essentially of a mixture of propylene and n-pentane.

5. In a continuous mass polymerization process wherein liquid propylene is contacted in a polymerization zone with a catalyst formed by mixing materials consisting essentially of (a) a dialkylaluminum chloride and (b) the reduction product obtained by reacting titanium tetrachloride and aluminum, under polymerization conditions so as to form solid polymer in particle form and wherein an efiiuent containing solid polymer catalyst residues and liquid propylene is recovered from said polymerization zone, the improvement which comprises introducing said effluent into a contact zone; mixing said efiluent in said contact zone with acetylacetone, said mixing occurring under conditions such that said propylene remains in liquid phase; withdrawing the thus treated efliuent from said contact zone, introducing said treated effluent into an upper portion of a wash zone; introducing a wash liquid consisting essentially of liquid propylene into a lower portion of said wash zone; contacting said treated efliuent with said liquid propylene in said wash desired level of polymer solids is maintained in the bottom portion of the wash tank.

Upon passing through valve 49, which operates as a pressure letdown valve, the polymer slurry flashes as it passes into flash tank 54. In the flash tank the pressure may range from 16 to 65 p.s.i.g. while the temperature may be in the range of 50 to 15 F. The propylene Which flashes olf is Withdrawn from the flash tank through line 56 and then passed into cyclone separator 57. In the cyclone separator, any solid material contained in the gaseous propylene stream is recovered as underflow through line 58 and is usually discarded. The gaseous propylene is recovered as the overflow through line 59. The gaseous propylene is thereafter reused in the process after being subjected to suitable purification operations.

Solid polymer in particle form and containing residual amounts of propylene is withdrawn from the bottom of flash tank 54 and falls into drier-conveyor 61. This conveyor is equipped with a jacket through which hot water or other suitable heat exchange fluid can be circulated. The heat exchange fluid is introduced into the jacket through line 62 and is withdrawn therefrom through line 63. Conveyor 61 is provided with an anger 64 which is powered by a motor 66. As the polymer solids are moved through the conveyor by means of the auger, propylene is evaporated as a result of the heat added to the moving polymer by the hot water circulating through the jacket. The propylene vapors are removed from conveyor 61 through line 67. This gaseous propylene can thereafter be suitably treated and reused in the process. After the polymer solids are conveyed to the end of conveyor 61, they are passed through rotary valve 58 positioned in conduit 69. The polymer solids then drop into purge conveyor 72 which contains an auger '73 driven by a motor 74. As the polymer solids are moved through conveyor 72, they are contacted with a heated non-combustible gas introduced through line 75. Any suitable non-combustible gas, such as carbon dioxide, nitrogen, or the like, can be utilized. In flowing through conveyor 72, the gas contacts the polymer solids as they are moved therethrough, thereby evaporating residual amounts of propylene and also purging previously evaporated propylene. The gases are withdrawn from conveyor 72 through line 77 after which they can be passed to a flare. Polymer solids, substantially free of propylene and having an ash content of less than about 0.01 weight percent, are recovered from purge conveyor 72 through line 78. The polymer so recovered can then be transferred to suitable storage facilities or to subsequent operations such as packaging or pelleting.

The polypropylene product prepared in accordance With this invention has utility in applications where solid plastics are employed. The polymer can be molded to form articles of any desired shape such as bottles and other containers for liquids. Furthermore, the product can be formed into fibers and pipe by extrusion.

A more comprehensive understanding of the invention can be obtained by referring to the following illustrative example which is not intended, however, to be unduly limitative of the invention.

EXAMPLE Propylene is polymerized in a mass polymerization in the presence of hydrogen and utilizing a catalyst consisting of diethylaluminurn chloride and a titanium trichloride complex. The titanium trichloride complex is prepared by reacting titanium tetrachloride with aluminum, and the complex comprises 4.74 weight percent aluminum, 25.0 weight percent titanium, and 69.8 weight percent chlorine. The product obtained from he polymerization is thereafter treated in accordance with the present invention so as to obtain a polymer product having a very low ash content. The polymerization and the treatment of the polymer are conducted in equipment similar T0 to that shown in the drawing and the details of the process are described hereinafter in conjunction with the drawing.

A purified feed stream of liquid propylene is charged to loop reactor 10 through line 11. The titanium trichloride complex and the diethylaluminum chloride are introduced into the reactor through lines 12 and 13. Hydrogen enters the reactor along with the propylene after being introduced into the propylene feed line through line 14. The loop reactor is operated at a temperature of F. and a pressure of 370 p.s.i.a. The polymerization temperature is maintained at 130 F. by circulating water through the heat exchange jackets with which the loop reactor is provided. The residence time of the reactant materials in the loop reactor is about 3 hours. An effluent stream containing solid polymer in particle form, liquid propylene, catalyst residues and soluble polymer is removed from the loop reactor through line 27. This eflluent stream contains about 25 weight percent solid polymer.

The eflluent stream recovered from the loop reactor is then passed into contact tank 29. Prior to entering the contact tank, a one weight percent solution of acetylacetone in propylene is added to the stream. In the contact tank, the solid polymer is brought into intimate contact with the acetylacetone. The contact tank is operated at a temperature of F. and a pressure of 370 p.s.i.a. The temperature in the contact tank is maintained at 140 F. by introducing heated n-pentane into the tank through line 34. After a contact time of 30 minutes, the treated eifluent stream is passed into wash tank 41. In the wash tank, the treated efliuent stream is contacted in countercurrent flow with liquid propylene charged to the tank through line 42. About 12 pounds of liquid propylene per pound of polymer is employed as the was-h liquid. A stream containing liquid propylene, catalyst residues and soluble polymer is taken overhead from the wash tank through line 43 and thereafter passed into cyclone 44. Solid polymer carried over in the overhead stream is se arated out in the cyclone and returned to the wash tank through line 46. The overflow from the cyclone is recovered through line 47, and the rate of withdrawal of the overflow is controlled by reactor valve 50 which operates so as to maintain a pressure of 370 p.s.i.a. in the loop reactor. A slurry containing about 50 weight percent solid polymer in liquid propylene is withdrawn from the bottom of wash tank 41 through line 48. The rate of withdrawal of the solid polymer is controlled by means of a cyclically operated motor valve 49. After passing through motor valve 49, the slurry of solid polymer in liquid propylene passes into flash tank 54 which is operated at a tempera ture of 32 F. and 25 p.s.i.a. The propylene flashes off and is removed from the flash tank through line 56. After separation of any solids contained in the gaseous propylene by means of cyclone 57, the material is then treated prior to reuse in the process.

Solid polymer containing residual propylene drops from the bottom of flash tank 54 into drier-conveyor 61. In the conveyor, the polymer is heated by means of hot water which is circulated through the jacket with which the conveyor is equipped. As a result of this heating, propylene is evaporated and then removed through line 67. Polymer solids fall through conduit 69 attached to the end of conveyor 61 and then enter purge conveyor 72. In the purge conveyor, the polymer solids are contacted with nitrogen which functions as a purge gas to remove any remaining propylene. Solid propylene in particle form, which is recovered from the purge conveyor through line 78, is thereafter passed to suitable storage facilities. The polypropylene so recovered contains less than 0.01 weight percent ash. The various flow rates employed in the above-described process are shown hereinbelow in the table. The rates shown in the table are in pounds per stream day, and the stream numbers refer to the line numbers shown in the drawing.

zone in countercurrent flow under conditions such that said propylene remains in liquid phase; withdrawing from an upper portion of said wash zone a stream comprising propylene, soluble polymer and catalyst residues; and recovering from a lower portion of said wash zone a stream comprising propylene and solid polymer substantially free of catalyst residues.

6. The process according to claim in which said polymerization occurs at a temperature in the range of 90 to 160 F. and at a pressure sufiicient to maintain said propylene in liquid phase; and said contact zone is maintained at a temperature in the range of 100 to 170 F. and at a pressure sufiicient to maintain said propylene in liquid phase.

7. The process according to claim 6 in which a. heated low boiling hydrocarbon is charged to said contact zone at a rate and at a temperature such as to maintain therein a temperature in said range of 130 to 150 F.

8. The process according to claim 7 in which said low boiling hydrocarbon consists essentially of propylene.

9. The process according to claim7 in which said low boiling hydrocarbon consists essentially of n-pentane.

10. The process according to claim 5 in which a stream comprising propylene, catalyst residues and soluble polymer is recovered from an upper portion of said wash zone and said stream is withdrawn at a rate such as to maintain a predetermined polymerization pressure in the range of 275 to 1000 p.s.i.g.

11. The process according to claim 5 in which said stream recovered from a lower portion of said wash zone is introduced into a flash zone; gaseous propylene is withdrawn from an upper portion of said flash zone;

and solid polymer in particle form and containing residual propylene is recovered from a lower portion of said flash zone.

12. The process according to claim 5 in which said acetylacetone is introduced into said contact zone as a solution in propylene.

13. The process according to claim 5 in which said stream recovered from a lower portion of said wash zone is withdrawn in cycles, thereby causing turbulence in said zone.

14. The process according to claim 5 in which said stream recovered from a lower portion of said wash zone is withdrawn at a rate such as to maintain a desired level of polymer solids in said lower portion of said wash zone.

References Cited by the Examiner UNITED STATES PATENTS 2,783,884 3/1957 Sehaub 134 25 2,971,951 2/1961 Cines 260-94.9 2,982,763 5/1961 McLeod 260-249 2,996,492 8/1961 Tegge et al. 26094.9 3,002,961 10/1961 Kerschner et al. 26094.9 3,066,124 11/1962 Telfer 26094.9

FOREIGN PATENTS 571,762 3/1959 Canada.

JOSEPH L. SCHOFER, Primary Examiner.

MORRIS LIEBMAN, Examiner.

D. E. OLSON, E. M. OLSTEIN, F. L. DENSON,

Assistant Examiners. 

